A long-range acoustic device has been developed by American Technology Corporation to repel pirates.

The portable device, with a range up to 300m, weighs 20kg and can emit sounds at volumes that can permanently damage hearing.

The warning, which can also blur vision, uses a high-pitched shrill similar to that of a home smoke alarm.

Users of the device will be protected by wearing earplugs, headsets or head phones which can bring the noise down to low levels.

The sound of the device can also be reflected back from a solid surface and come back to the operator, if not handled carefully.